Frequency sensitive preionizer

ABSTRACT

This frequency sensitive preionizer uses integrated circuitry in providing a resistance, a capacitance, and a preionizing spark gap deposited on an insulating base. The capacitance is connected in series with a parallel combination of the preionizing spark gap and the resistance, and impulse overvoltages are readily conducted by the capacitance causing the preionizing spark gap to emit photons for initiating preionization of a spark gap prior to sparkover.

United States Patent Kresge et al.

1 1 Oct. 29, 1974 Stetson 315/36 Carpenter 315/36 Primary Examiner James W. Lawrence Assistant Examiner-Saxfield Chatmon, Jr.

Attorney, Agent, or FirmV01ker R. Ulbrich; Francis X. Doyle; John J. Kel1eher [57] ABSTRACT This frequency sensitive preionizer uses integrated circuitry in providing a resistance, a capacitance, and a preionizing spark gap deposited on an insulating base The capacitance is connected in series with a parallel combination of the preionizing spark gap and the resistance, and impulse overvoltages are readily conducted by the capacitance causing the preionizing spark gap to emit photons for initiating preionization of a spark gap prior to sparkover.

5 Claims, 6 Drawing Figures 1 FREQUENCY SENSITIVE PREIONIZER BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to overvoltage protective devices and more particularly to frequency sensitive preionizers for use in such overvoltage protective devices.

2. Description of the Prior Art A spark gap is a well-known overvoltage protective device. The spark gap is formed by ionized pair of spaced electrodes with one of the electrodes being connected to ground and the other electrode being connected to an electrical conductor which the spark gap is to protect against overvoltages. An overvoltage applied to the conductor causes the spark gap to spark over and conduct this overvoltage to ground, but normal operating voltages on the conductor are insufficient to cause sparkover. Because it is desired to remove only overvoltages from the conductor, the spark gap device must spark over at a precise and predictable voltage magnitude greater than the normal operating voltage. A preionizer is a device which secures this predictable performance. A preionizer is used in conjunction with a spark gap to inject a photon or quantum of energy into the spark gap. The photon, upon striking one of the charged electrodes of the spark gap, causes ions or electrons to be emitted which ionize the medium between the electrodes of the spark gap. An ionized medium between the electrodes will readily conduct and support sparkover when the voltage between the electrodes exceeds a predetermined magnitude. Without a preionizer, sparkover would depend greatly upon the probability that a naturally occurring ion or photon would initiate ionization of the medium in the spark gap. The undependability of naturally occurring photons causes a wide fluctuation in the voltage at which a non-preionized spark gap sparks over, and pre dictable sparkover performance is almost impossible with a non-preionized spark gap. Thus, a preionizer is essential in providing reliable overvoltage protection.

One type of preionizer known in the art is a field sensitive preionizer. The field sensitive preionizer is responsive to the voltage sensed between the electrodes of the spark gap and emits photons after the voltage between the electrodes has risen above the normal operating level. However, it is extremely difficult to produce voltage responsive characteristics in the field sensitive preionizer which are consistent and predictable. Consequently, the voltage at which the field sensitive preionizer begins to emit photons may fluctuate within a wide range, and many times the field sensitive preionizer has failed to preionize the spark gap when the spark gap is required to spark over. Because of these factors, prior art field sensitive preionized spark gaps have failed to provide precise overvoltage protection.

in many cases, such as in the case of cascade gaps in a lightning or surge arrester, the overvoltage for which a gap is required to sparkover is always a fast impulse. For such a gap a type of preionizer which solves the erratic performance problems of the field sensitive preionizer is a frequency sensitive preionizer. In its most generalized form. the frequency sensitive preionizer is a frequency sensitive circuit which responds only to impulse overvoltages by producing photons to ionize the spark gap but remains inoperative at low frequencies, such as the normal Hz. electrical supply frequency. Electrical theory holds that an impulse is comprised of a number of very high frequencies, and a circuit which will respond to very high frequencies will likewise respond to an impulse. The frequency sensitive preionizer senses the very high frequencies of the impulse overvoltage and responds by emitting photons. As the overvoltage continues to rise in magnitude, the overvoltage attains a level at which sparkover occurs and the overvoltage is removed from the conductor. Thus, the frequency sensitive preionizer is actually impulse sensitive.

The foregoing description readily illustrates the advantages of a frequency sensitive preionizer over a field sensitive preionizer. The frequency sensitive preionizer, being impulse responsive, provides the inherent advantage of consistent preionization only during an impulse type of overvoltage, which is the only time some gaps are required to sparkover. Thus frequency sensitive preionizers provide reliable sparkover of such gaps, for example cascade gaps.

The present invention provides the desirable performance of a frequency sensitive preionizer and is also of a construction which allows adequate control of the values of the frequency sensitive elements for reliable operation. The small and compact construction allows the frequency sensitive preionizer to be manufactured separately from the spark gap assembly, and the structure of the preionizer is such that it allows the spark gap assemblies to be serially stacked to form a spark gap arrestor.

SUMMARY OF THE INVENTION It is an object of this invention to provide a frequency sensitive preionizer which reliably and consistently initiates ionization of a spark gap under the influence of a surge or impulse overvoltage.

It is another object of this invention to provide a frequency sensitive preionizer having frequency sensitive elements adequately controlled to provide reliable operational characteristics of the preionizer and the spark gap in reponse to impulse type overvoltages.

It is a further object of this invention to provide a small and compact frequency sensitive preionizer which allows it to be easily used in a spark gap assembly.

It is still another object of this invention to provide a frequency sensitive preionizer which may be manufactured as a unitary structure separate from a spark gap assembly and may thereafter be easily combined as a component of a spark gap arrestor.

To achieve these and other objects, in one form of the invention the frequency sensitive preionizer comprises an insulating base having first and second sides on which first and second preionizer electrodes, respectively, are deposited in the form of an integrated circuit. A plate of metallic material is deposited on the first side. and capacitance is formed by a portion of the second preionizer electrode, the plate, and the base therebetween. A resistive element is also deposited on the first side and electrically interconnects the metallic plate and the first preionizer electrode. A preionizing spark gap separates the plate from the first preionizer electrode. This arrangement provides an integrated, frequency sensitive circuit having the capacitance electrically connected in series with a parallel combination of the preionizing spark gap and the resistive element. This frequency sensitive circuit causes the preionizing spark gap to spark over and emit photons for initiating ionization of the spark gap when the circuit is subjected to an impulse or surge overvoltage, because the low impedance of the capacitance to the high frequencies in herent in the impluse overvoltage causes the overvolt age to appear across the resistive element and the preionizing spark gap, thereby causing the preionizing spark gap to spark over and emit photons.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the invention may be had by referring to the accompanying detailed description and drawings in which:

FIGS. la and lb are top and side views, respectively, of the preferred embodiment of a frequency sensitive preionizer incorporating this invention;

FIG. 2 is a schematic diagram of the invention;

FIGS. 30 and 3b are partial top and side views of the frequency sensitive preionizer of this invention as employed in a spark gap assembly; and

FIG. 4 is a perspective view of a number of serially stacked spark gap assemblies employing such frequency sensitive preionizers.

DETAILED DESCRIPTION OF THE INVENTION A preferred embodiment of a frequency sensitive preionizer I is illustrated in FIGS. la and lb. The preionizer includes a base 12 constructed of insulating dielectric material, such as a ceramic material or other material typically used in integrated circuitry which has electrical insulating properties and to which integrated electronic elements may be secured. As best seen in FIG. lb, the base has a first side 14 and a second side 16 which may occupy parallel planes displaced from one another by the thickness of the base as reflected by the thickness dimension 18. A first preionizer electrode 20 and a second preionizer electrode 22 are deposited on the first side 14 and the second side 16, respectively, of the base 12, as seen in FIGS. la and lb. The preionizer electrodes 20 and 22 are deposited on the base I2 by well-known methods employed in integrated circuitry for depositing integrated electronic elements to a base. As employed in carrying out this invention, depositing is intended to include vapor depositing, glue ing or any other known method of incorporating electronic components in an integrated circuit.

In the integrated circuit construction of this invention, a capacitance can be conveniently provided by a plate 24 of metallic material deposited on the first side 14 of the base 12, a portion 220 of the second preionizer electrode 22, and the base material therebetween. The plate 24 and the portion 220 may be directly opposite in position on the first and second sides, respectively, ofthe base 12, as is best seen in FIG. lb, and are, therefore, separated or spaced by that amount of insulative dielectric material as measured by the thickness dimension 18 of the base l2.

The plate 24 on the first side of the base is spaced from the first preionizer electrode 20 a predetermined distance, as best shown in FIG. la, thereby forming a preionizing spark gap 26 between the first preionizer electrode 20 and the plate 24. The plate 24 is electrically interconnected by a resistive element 28 to the first preionizer electrode 20. The resistance element 28 is any well-known resistance material used in integrated circuitry and is deposited on the first side 14 of the base I0 in a manner similar to that previously described.

The foregoing elements from a frequency sensitive preionizer having a schematic circuit diagram shown in FIG. 2. The same reference numerals are used to designate corresponding elements in FIG. 2 and in the other Figures employed to describe this invention. The frequency sensitive preionizer is used in conjunction with a main spark gap 30 formed by a pair of spaced main spark gap electrodes 32 and 34, which make up spark gap assembly 36. The first preionizer electrode 20 is electrically connected to one of the main spark gap electrodes, for example 32, by an electrical conductor 38. The second preionizer electrode 22 is connected to the other main spark gap electrode, for example 34, by another electrical conductor 40. The plate 24 and the portion 220 of the second preionizer electrode 22 form a capacitance or other similar frequency sensitive impedance element which exhibits low impedance to high frequencies and high impedance to low frequencies. The capacitance is electrically connected in series with the preionizing spark gap 26 or other similar means for emitting photons and projecting the photons onto at least one of the main spark gap electrodes. The capacitance and preionizing spark gap are electrically connected between the pair of main spark gap electrodes 32 and 34, and the resistive element 28 is electrically connected in parallel with the preionizing spark gap 26. Connected in this manner, the frequency sensitive preionizer 10 will emit photons to initiate ionization of the main spark gap 30 upon the occurrence of an impulse overvoltage.

The operation of the frequency sensitive preionizer will now be described in conjunction with FIG. 2. Under normal operating voltage magnitudes and frequencies, the voltage appearing across the main spark gap 30 is insufficient to cause the main spark gap 30 to spark over. The capacitance exhibits a very high impedance at normal operating frequencies, causing substantially all the voltage across the main spark gap 30 to appear across the capacitance and very little or no voltage to appear across the resistive element 28 or the preionizing spark gap 26. Thus, at normal frequency and magnitude levels, the preionizing spark gap 26 does not spark over to emit photons to preionize the main spark gap 30. Upon the occurrence of an impulse overvoltage, the high frequencies of the impulse are readily conducted by the capacitance which exhibits low impedance to the high frequencies, and substantially the total magnitude of the impulse overvoltage is present across the resistive element 28 and the preionizing spark gap 26. The magnitude of the impulse overvoltage causes the preionizing spark gap 26 to spark over and emit photons to preionize the main spark gap 30. The precisely controlled, predetermined width of the preionizing spark gap 26, being less than the width of the main spark gap, results in sparkover and photon emission before the impulse overvoltage has reached a magnitude at which the main spark gap 30 sparks over. Upon the impulse overvoltage reaching a magnitude sufficient to cause the main spark gap 30 to spark over, the photons from the frequency sensitive preionizer have readied the main spark gap for reliable and accurate sparkover. Thus, the main spark gap 30 is preionized before it sparks over.

Moreover, this integrated circuit construction lends itself to ready incorporation in a spark gap assembly. This aspect of the invention is shown in FIGS. 30 and 3b where the frequency sensitive preionizer is illustrated in conjunction with the main gap 30. The main spark gap 30 is formed by the pair of spaced main spark gap electrodes 32 and 34 mounted within an insulating housing 42 to form a spark gap assembly 36. Retaining means such as the bolts 44 attach the main spark gap electrodes 32 and 34 to the housing 42, and electrically connect the stacked spark gap assemblies in series to form a spark gap arrestor. The first and second preionizer electrodes are adapted to be connected to the main spark gap electrodes 32 and 34 by the electrical conductors 38 and 40. FIG. 3b illustrates in a side view how the compact and concisely constructed preionizer has a low profile which eliminates any problems in stacking the spark gap assemblies 36 to form a spark gap arrestor. In addition, the electrical conductors 38 and 40 readily connect the frequency sensitive preionizer to the spark gap assembly and allow the preionizer to be manufactured as a unitary structure separate from the spark gap assembly. FIG. 4 shows how a plurality of spark gap assemblies 36, employing the frequency sensitive preionizers 10 of this invention, may be stacked together very compactly to form a spark gap arrestor.

Proper operation of the frequency sensitive preionizer requires that its resistive-capacitive time constant must be greater than a microsecond so as to provide sufficient sparkover current for the preionizing spark gap, and much less than 4167 microseconds, the quarter period of a 60 Hz. electrical supply, so as to distinguish impulse overvoltages from the normal electrical supply frequency. In a specific embodiment of the invention, the base of the preionizer was formed from a ceramic slab having a thickness of 0.055 inch which resulted in a capacitance in the range of 0.1 to l picofarad. Of course, the value of the capacitance may be changed by merely varying the thickness of the base or by varying the area of the plate 24 or of the portion 220 of the second preionizing electrode 22 forming part of the capacitance. Well-known resistive materials easily provide a value of l to l00 megaohms for the resistive element, thereby insuring that the time constant falls within the range indicated. It was also found that the width of the preionizing spark gap secures the best performance when in the range of 0.005 to 0.010 inch.

Constructing the resistive and capacitive elements and the width of the preionizing spark gap by integrated circuit methods assures reliable performance during impulse overvoltage conditions at the instant when the spark gap is required to provide overvoltage protection. Furthermore, because of the small and compact construction of the frequency sensitive preionizer, it is easily inserted and employed within the stacked spark gap assemblies forming a spark gap arrestor.

Although a single embodiment of the frequency sensitive preionizer has been shown and described, those skilled in the art will perceive changes and modifications without departing from the invention. Therefore, it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A preionizer for a main spark gap formed by a pair of spaced main spark gap electrodes comprising:

a. a base of insulating dielectric material having a first and a second side; b. a first preionizer electrode of metallic material deposited on the first side of said base and being adapted to be electrically connected to one of the main spark gap electrodes; c. a second preionizer electrode of metallic material deposited on the second side of said base and being adapted to be connected to the other main spark gap electrode; d. a plate of metallic material deposited on the first side of said base, said plate and a portion of said second preionizer electrode and the insulative dielectric material therebetween defining a capacitance,

said plate being spaced from said first preionizer electrode a predetermined distance to form a preionizing spark gap therebetween;

e. a resistive element of resistance material deposited on the first side of said base and electrically interconnected between said plate and said first preionizer electrode, whereby the capacitance is electrically connected in series with a parallel combination of the preionizing spark gap and the resistive element to form a frequency sensitive preionizer.

2. The preionizer as recited in claim 1 wherein:

a. the first and second sides of said base occupy parallel planes displaced by the thickness dimension of said base; and

b. said plate and a portion of the second preionizer electrode are directly opposite in position on the first and second sides of said base, respectively.

3. A preionizer for a main spark gap formed by a pair of spaced main spark gap electrodes comprising:

a. a frequency sensitive impedance element exhibiting low impedance to high frequencies and high impedance to low frequencies;

b. means for emitting photons which are projected onto at least one of the main spark gap electrodes;

said frequency sensitive impedance element and said means for emitting photons being electrically connected in series between the pair of main spark gap electrodes, whereby the low impedance of said frequency sensitive element to high frequencies of an impulse overvoltage activates said means for emitting photons and the photons cause at least one of the main spark gap electrodes to emit electrons or ions to ionize the main spark gap prior to sparkover.

4. The frequency sensitive preionizer as recited in claim 3 wherein said frequency sensitive impedance element is a capacitance and said means for emitting photons is a preionizing spark gap.

5. The frequency sensitive preionizer as recited in claim 4 wherein a resistive element is electrically connected in parallel with the preionizing spark gap.

t a: m 

1. A preionizer for a main spark gap formed by a pair of spaced main spark gap electrodes comprising: a. a base of insulating dielectric material having a first and a second side; b. a first preionizer electrode of metallic material deposited on the first side of said base and being adapted to be electrically connected to one of the main spark gap electrodes; c. a second preionizer electrode of metallic material deposited on the second side of said base and being adapted to be connected to the other main spark gap electrode; d. a plate of metallic material deposited on the first side of said base, said plate and a portion of said second preionizer electrode and the insulative dielectric material therebetween defining a capacitance, said plate being spaced from said first preionizer electrode a predetermined distance to form a preionizing spark gap therebetween; e. a resistive element of resistance material deposited on the first side of said base and electrically interconnected between said plate and said first preionizer electrode, whereby the capacitance is electrically connected in series with a parallel combination of the preionizing spark gap and the resistive element to form a frequency sensitive preionizer.
 2. The preionizer as recited in claim 1 wherein: a. the first and second sides of said base occupy parallel planes displaced by the thickness dimension of said base; and b. said plate and a portion of the second preionizer electrode are directly opposite in position on the first and second sides of said base, respectively.
 3. A preionizer for a main spark gap formed by a pair of spaced main spark gap electrodes comprising: a. a Frequency sensitive impedance element exhibiting low impedance to high frequencies and high impedance to low frequencies; b. means for emitting photons which are projected onto at least one of the main spark gap electrodes; said frequency sensitive impedance element and said means for emitting photons being electrically connected in series between the pair of main spark gap electrodes, whereby the low impedance of said frequency sensitive element to high frequencies of an impulse overvoltage activates said means for emitting photons and the photons cause at least one of the main spark gap electrodes to emit electrons or ions to ionize the main spark gap prior to sparkover.
 4. The frequency sensitive preionizer as recited in claim 3 wherein said frequency sensitive impedance element is a capacitance and said means for emitting photons is a preionizing spark gap.
 5. The frequency sensitive preionizer as recited in claim 4 wherein a resistive element is electrically connected in parallel with the preionizing spark gap. 